plant fungi – Extension Master Gardener Volunteers of Durham County

By Wendy Diaz, NC State Extension Master Gardener^SM volunteer of Durham County

Evidence of Cedar-Quince Rust on Eastern Redcedar (Juniperus virginiana)

I noticed a bright orange coating on the peeling bark of the branches and trunk of an Eastern Redcedar shrub (Juniperus virginiana) along my backyard property boundary during a routine walk around my yard in the early spring last year.

Orange swellings between peeling and on bark of Eastern Redcedar branch on March 13, 2025. (Image credit: Wendy Diaz)

Many years ago, I transplanted it along with several other volunteer Eastern Redcedar seedlings, to create a windbreak and evergreen screen when the hardwood forest behind our property was developed into a subdivision. I knew at the time it wasn’t an ideal location for these sun-loving natives[1]; under the shade of a large White Oak but they did survive and slowly grew from 4 inches to several feet high.

View of backyard Eastern Redcedar hedge. Area circled in red denotes the diseased cedar shrub planted behind the white oak tree which was diseased and later removed. (Image credit: Wendy Diaz)

The Eastern Redcedar with the orange coating was located in the most-shaded part of the hedge and behind the oak, so it was no surprise to me that it developed a disease at this location. There are three different rust fungus that can infect Eastern Redcedar: 1. Gymnosporangium juniperi-virginianae[2] which produces bright orange gelatinous galls with tendril-like protrusions or Cedar-Apple Rust (spores from these galls will infect apple trees). 2. Gymnosporangium globosum smaller, less conspicuous branch galls, with horn-like protrusions or Hawthorne Rust and, 3. Gymnosporangium clavipes or Quince rust (spores infect rosaceae plants). I did not observe round branch galls[3] so I concluded Cedar-Quince rust was the disease on my cedar shrub which is caused by the Gymnosporangium globosum fungus[4].

Close up of Cedar-Quince Rust on branch of Eastern Redcedar on March 13, 2025. (Image credit: Wendy Diaz)

Disease Cycle

These fungi need plants from two plant families to complete their life cycle (multiple hosts).[5] Of the rust diseases, Cedar-Quince has the broadest host range and affects many genera of the Rosaceae family including apple, crabapple, flowering quince, hawthorn, serviceberry and mountain ash.[6] In damp spring weather it forms orange, gelatinous blisters on the bark of branches of the Eastern Redcedar. It can kill young branches and weaken plants when the cankers develop on the main trunk. When it infects the other hosts, like apple, it infects the young branches and fruit but not the leaves. Basidiospores released from the Eastern Redcedar branch orange swellings will infect the stems and fruit of quince and other deciduous host plants. Seven to ten days after infection spots develop, followed by the formation of tiny black dots within the spots a few days later. Globular or cup-shaped structures (aecia) are formed four to seven weeks later. Aecipospores, which are released during a rain event from these structures, will become airborne and infect susceptible Easter Redcedar plants during late summer or fall. One year later, swellings composed of both fungal and host plant tissues will develop on the Eastern Redcedar host. When the spring weather is wet and cool (74 to 78 degrees F) swelling on the branches of the Eastern Redcedar will result in the release of basidiospores which in turn will infect quince or another deciduous host, and the cycle continues.

Management of Cedar-Quince Rust on Eastern Redcedar

Pruning and proper disposal of the infected branches, if practical, is a good way to control the disease. I decided to remove the thinly branched Eastern Redcedar and burn it because it had lost it ornamental value and it was unhealthy and the other cedars beside it did not appear to be infected. Because two kinds of plants are necessary for the survival of this fungus, removal of my old flowering quince in my front yard that has developed galls seems to be a practical solution for me because I want to eventually remove most of my non-native species in my yard.[7]

There are preventive fungicides that are made to protect developing/new growth twigs and branches from infection during the time the swellings on the Eastern Redcedar are orange and gelatinous. Multiple applications over several weeks are necessary until the orange coating becomes dry and inactive. Pesticides registered for use include: captan, chlorothalonil, mancozeb, sulfur, thiram and ziram. Other strategies include not planting susceptible host plants within a few hundred yards of apples, hawthorns and other plants of the Rosaceae family. Other cultural methods of disease control would be planting plants that are resistant to rust diseases and removing galls from the deciduous host plants to reduce infection of the alternate host plant. The gall is not as big as the black knot disease[8].

Black gall on the flowering quince on Febraury 24, 2025. The gall is not as big as those associated with black knot disease.⁸(Image credit: Wendy Diaz)

This experience was a reminder to me to take a stroll and inspect parts of my yard that I have taken for granted and it was well worth the time because the other adjacent Eastern Redcedar shrubs in my border screen do not exhibit any fungal rust symptoms. Scouting for disease is good gardening practice. You know what they say ‘an ounce of prevention is worth a pound of cure’. If you have Eastern Redcedar trees in your yard now is the time to inspect for any evidence of fungal rust disease. Your neighbor with a flowering crabapple may thank you.

Notes

[1] https://plants.ces.ncsu.edu/plants/juniperus-virginiana/

[2] https://hgic.clemson.edu/factsheet/juniper-diseases-insect-pests/

[3] https://content.ces.ncsu.edu/extension-gardener-handbook/5-diseases-and-disorders#section_heading_7616

[4] tps://ask2.extension.org/kb/faq.php?id=828832

[5] https://hgic.clemson.edu/factsheet/cedar-apple-rust/

[6] https://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/insects-pests-and-problems/diseases/rusts/cedar-quince-rust

[7] https://extension.umn.edu/plant-diseases/cedar-apple-rust

[8] https://hyg.ipm.illinois.edu/pastpest/200715b.html

Resources and Additional Information

Read about another fungal disease that affects trees (Black Knot Disease: Apiosporina morbosa ) in a previous post by Melinda Heigel: https://durhammastergardeners.com/wp-admin/post.php?post=15569&action=edit

The links highlighted in the notes are excellent resources for learning more about fungal rust that can infect the Eastern Redcedar.

Article Short Link: https://wp.me/p2nIr1-5GL

By Eric Wiebe, NC State Extension Master Gardener^SM volunteer of Durham County

(Image credit: Allie Mullin)

As the gardening season is winding down, it’s time to start thinking about your fall and winter tasks. Near the top of that list should be thinking about mulching your plantings. A tour of your yard will probably reveal thin or bare spots where last year’s mulch has either broken down or been washed or blown away (those darn leaf blowers!). You may also want to put a winter cover on areas where you had vegetables growing. Finally, you may also have new areas you are preparing as garden beds where mulch will need to go around the new plantings.

Why Mulch Matters

First, let’s review why you want to be mulching in the first place. The primary reason most people mulch is for a combination of weed suppression and moisture retention. However, there are other just as important reasons to mulch. If you are using organic materials, you have the important benefit of in-place composting and humus generation, improving the biodiversity of the ground ecosystem throughout the mulch and into the surrounding soil and plants. Depending on type and placement, mulch can also help with erosion control and compaction. In addition to absorbing and holding moisture from rainfall, it can also minimize water splash from the underlying soil onto plants–potentially limiting the spread of harmful soil-borne fungi, such as blight. Finally, there may be good aesthetic reasons to mulch to create sharp delineations in color and texture in the landscape.

Types of Mulching Materials

What kinds of materials can you mulch with? Broadly speaking, mulches are grouped into organic and non-organic types. Included in organic materials are natural products, primarily from trees, that have been processed but will readily decompose–this includes cardboard, newspaper, and other paper products.

Inorganic Mulch

The most common non-organic materials are landscape fabrics made from plastic–either sheet or woven–and various types of stone. These are often used together, as the landscape fabric can be placed under the stone to help suppress weeds and keep the stone from migrating into the soil. Plastic sheet, with or without perforations, is also used in fruit and vegetable production, often applied with specialized machinery. The rest of the blog post will focus on the more popular and beneficial organic mulches used by home gardeners.

Organic Mulch

While shredded hardwood comes to mind when thinking about mulch, other organic materials like leaves are great sources for mulching material. As they decompose, leaves improve soil health by providing nutrients and improving both water retention and percolation. (Left) Newly-raked leaves ready to be spread across the garden. (Right) Leaf mulch after a year of decomposing. (Image credit: Eric Wiebe)

Organic materials can be found from a variety of sources. The best and most convenient materials are those found right in your yard. This includes leaves, new or partially decomposed; grass clippings, compost, and plant and tree trimmings. There is the argument to be made that the best mulch sources are the most local, as they represent the local ecosystem and can best support the macro-/microbiome already in your yard.

(Left to right) Arborist chip drop ready to be spread and a close-up of this type of mulching material. (Image credit: Eric Wiebe)

If you don’t have enough organic sources of mulch within your own yard, consider arborist wood chips. These are the product of local tree services as they cut down and chip tree limbs and can be acquired for free through a national service, ChipDrop (https://getchipdrop.com/). This product is still relatively local, representing tree species from your area and, for most of the year, contains a mixture of bark, wood, and leaves.

Research has shown that wood chips perform well with regards to moisture retention, temperature moderation, and weed control. While you can buy shredded (often from grinding whole trees), bark, and sawdust mulches from garden centers, many of these products are imported from other areas, bagged in plastic, or dyed. All of these factors both increase your cost and reduce their sustainability. In contrast, the biochemical and physical diversity of arborist chips resists compaction and creates a more diverse habitat for insects and microorganisms. Over time, the bark, wood chips and leaf matter will decompose, adding nutrients to the soil.

Paper products like newspaper and cardboard have long been used for sheet mulching/lasagne gardening techniques. Here a homeowner is using cardboard shipping boxes stripped of labels and tape as a base layer to be covered by other natural mulching materials. (Image credit: Melinda Heigel)

There are many, many other types of organic mulches that can be used. Pine straw is popular in NC and can be very local if you have a lot of pine trees on your property. While compost can also be used as mulch, its cost typically prohibits its use over a large area. Finally, paper products in the form of cardboard, newspaper, and brown paper have long been used as a form of sheet mulching. Note that you typically have to cover these materials with a somewhat dense mulch (e.g., partially decomposed leaves) in order to hold it in place. While there has been some social media controversy over the use of cardboard, it is still generally believed to be a quality mulch material when applied properly. Note that you should carefully remove non-decomposable elements such as tape and staples, and avoid glossy, non-brown cardboard as they may contain unwanted inks and plastics. While grass clippings can be used as a mulch, it tends to decompose quickly, not drain well when wet or blow away when dry. They may also contain excessive fertilizer or herbicides. Instead, consider mulching it in place in the lawn.

Tips for Effective Mulching

There are best practices to consider when using any mulch, and some considerations for specific types of mulches. First, to the best of your ability, plan how much area you have to cover and what volume of mulch you need. As a rule of thumb, you will need 6 cubic yards of mulch to cover 1,000 sq ft at 2″ deep–you generally will want to keep your mulch 1-3″ thick. However, this thickness will be driven in part by the density of the mulch; how well it retains moisture and allows oxygen to pass through it. Lighter mulch material such as pine straw or newly raked up leaves can often be deeper, while wood chips should be around 2-3.” If mulch is piled too deep, is too fine, or retains too much water, air cannot penetrate the mulch layer and the mulch and underlying soil can be depleted of oxygen. Mulch decomposing in low oxygen (anaerobic) conditions will sour, or ferment, producing methanol and acetic acid, which can be toxic to plants.

(Left to right) A properly-mulched tree has a few inches of mulch that extend to the edge of the drip line (or area that mirrors the tree’s crown). The root flare is visible at the base of the tree, as mulch isn’t in direct contact with the trunk. By contrast, the tree on the right is an example of all-to-familiar over mulching. Known as “volcano mulching,” mounding mulch around the trunk is harmful to your tree, leading to its decline and possible death. (Image credit: Penn State Extension; Eric Wiebe)

For all plants and trees, make sure to apply mulch all the way out to the drip line as you want to provide weed suppression, moisture retention, and soil benefits to all of the roots of the plant. Trees are another case of the dangers of over or improper mulching. Mulch should not come in contact with the bark of the tree as it promotes the kind of dark, moist environments that allow harmful fungi to enter the tree through the bark. Think donuts rather than volcanoes when you mulch your trees.

Impact of Mulch on Soil Chemistry

Using pine straw mulch as an acidifier on blueberries. (Image credit: Eric Wiebe)

Mulches can influence soil chemistry. While most of the time, this is happening in a good way, you need to understand the properties of the mulch you are using. Pine straw and pine bark, for example, has a naturally low pH. While this may be a problem on some plants, you can use it to your advantage with acid-loving plants such as azaleas or blueberries. Organic mulches with a high carbon-to-nitrogen ratio, like sawdust, hardwood bark, or wheat straw, may induce a short-term nitrogen deficiency as it breaks down. If plants in the mulched area become chlorotic and growth slows, consider applying one to two pounds of nitrogen per 1,000 sq ft to compensate. Almost all mulches will have a very localized nitrogen deficiency at the boundary between the soil and mulch. However, this is good as it inhibits weed growth.

Many of the basics and a few of the nuances about mulching have been covered here. As with most aspects of gardening, you can, if you want, continue to go down the rabbit hole of the science of mulching. The resources below will get you started!

Resources and Additional Information

General guidelines on mulching trees and shrubs: https://extension.umd.edu/resource/mulching-trees-and-shrubs/

Mulching garden beds:

https://carteret.ces.ncsu.edu/2021/08/mulching-your-garden-beds

https://yardandgarden.extension.iastate.edu/how-to/using-mulch-garden

Benefits of using arborist wood chips: https://pubs.extension.wsu.edu/using-arborist-wood-chips-as-a-landscape-mulch-home-garden-series

Tips for mulching in the spring: https://ext.vt.edu/lawngarden/turfandgardentips/tips/Springtime_mulch.html

Comprehensive guide to mulching materials: https://extension.unh.edu/sites/default/files/migrated_unmanaged_files/Resource007193_Rep10385.pdf

Sheet mulching/lasagne gardening gardening with paper products: https://extension.oregonstate.edu/gardening/soil-compost/sheet-mulching-aka-lasagna-composting-builds-soil-saves-time

https://extensiongardener.ces.ncsu.edu/2020/01/sheet-mulching-2020-winter-piedmont-news/

Problems with over mulching: https://pender.ces.ncsu.edu/2020/10/can-too-much-mulch-killl-plants/

Article Short Link: https://wp.me/p2nIr1-5iR